| Loquat (Eribotrya japonica Lindl.) is very popular for their appealing flavor and richness in nutrient. While loquat is harvested in time between spring and summer, it is easily infected by postharvest disease and hard to storage. Anthracnose rot caused by Colletotrichum acutatum is the major postharvest fungal disease in loquat fruit. Low tempreture storage is traditional fruit preservation methods. However, loquat is susceptible to low temperature and it will bring unsatisfying chilling injury, thus destroy the quality. Therefore, appropriate methods for preventing loquat fruit from pathogens in transportation and reducing the loss are in urgent need for loquat fruit.The present study was designed to investigate the effects of hot air treatment and MeJA treatment on control action of anthracnose rot from the perspectives of pathogen growth and the possible induction mechanism involved. On the basis of the above content, we determined the difference between the two methods during the disease resistance. And it will contribute for the application of those treatment methods. The following indicate the results:(1) The condition of hot air control on anthracnose rot of loquat fruit inoculated by C. acutatum was investigated and optimized by response surface methodology (RSM) under different time and temperature combinations. The exprement design was applied with treatment temperature (from 40 to 50℃) and exposure time (from 1 to 5 h) as independent variables. And the lesion diameter of loquat after storage at 20℃ for 8 days as investigated responses. The adequacy of the model equation for predicting the optimum response values was verified by the validated data. The model is significant and it has a better goodness of fit according to the vertification. Meanwhile, we found that the treatment showed a clear influence on the fruit lesion diameter from the analysis of surface contour diagram. We filtered the optimum hot air temperature is 43℃, while the optimum exposure time is 3 h.(2) The effects of hot air treatment 43℃、3h on anthracnose rot caused by C. acutatum in postharvest loquat fruit and the possible mechanisms involved were investigated. The results showed that fruit treated with hot air had significantly lower natural disease incidence and smaller lesion diameter than the control fruit did. Hot air treatment remarkably enhanced activities of phenylalanine ammonia-lyase (PAL), chitinase, β-1,3-glucanase and polyphenol oxidase (PPO). In addition, this hot air treatment also induced the expression of four defense-related genes including EjPAL、EjPPO、 Ejperoxidase (POD) and EjHSP70. The in vitro exprements showed that 43℃ 3 h can inhibit the sprouting rate, germ tube length and mycelial growth rate. These results suggest that hot air treatment can enhance disease resistance of loquat fruit by directly inducing the activity and gene expression of defense-related enzymes and by inhibiting the growth of pathogens.(3) The study found that 10 μmol/L MeJA treatment resulted in significantly smaller lesion diameter and lower natural disease incidence compared with the control in loquat fruit. While defensing the disease, the MeJA treatment before challenging inoculation significantly induced the higher activites of chitinase, β-1,3-glucanase, PAL, POD and the content of total phenolic compounds compared with MeJA treatment or challenging inoculation alone during the storage in loquat fruit. What’s more, MeJA treatment also induced the expression of the defense-related genes EjPAL2、EjPOD、EjPPO、EjERSl and EjNPRl-like. The influence is in consistent with the activities of defense-related enzymes. Simultaneously, the in vitro experiment showed that MeJA was not directly capable of inhibiting spore germination and germ tube elongation of C. acutatum. Thus, these results suggest that MeJA can effectively reduce fruit decay possibly by priming action, rather than a direct inhibitory effect on pathogen growth. |
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